Phase-sensitive measurements of depth dependent signal transduction in the inner plexiform layer

Phase-sensitive optical coherence tomography (OCT) is emerging as an imaging modality that detects functional changes in the retina. Besides imaging photoreceptor function, recently, functional changes in the inner plexiform layer (IPL) have been detected using full-eld swept-source OCT. The IPL connects neuronal cells which are dedicated for processing dierent aspects of the visual information, such as edges in the image or temporal changes. A characteristic of signal processing in the IPL is that dierent aspects of the visual impression are only processed in very specic depths. Here, we present an investigation of these functional signals for dierent depths in the IPL with the aim to separate dierent properties of the visual signal processing. Therefore, we investigate the phase changes of three dierent sub-layers. Whereas the rst two depths, closest to the ganglion cell layer, exhibit an increase in the optical path length, the third depth, closest to the bipolar cell layer, exhibits a decrease in the optical path length. Additionally, we found that the second or middle depth is sensitive to temporal changes, showing a maximum increase of the optical path length at a stimulation frequency of around 10 Hz. The results suggest that the responses from dierent cell types, which are sensitive to dierent features of the stimulation signal, can be distinguished by phase-sensitive OCT.